The invention relates to a melting end for glass melting furnaces having an end chamber for containing molten glass, having soldier blocks arranged side by side consisting of a refractory mineral material and surrounding the end chamber, with an inner side facing the end chamber, an outer side facing away from the end chamber, and a rectangular cross section at least in their lower region, and projecting upward above the established surface of the molten glass, the melting end also having cooling air nozzles which in the upper area of the soldier blocks are aimed at the outer side of the latter.
The said soldier blocks usually are in the shape of parallelepipedons whose longest axis is vertical and which surround the chamber in a gap-less and continuous row. The soldier blocks are usually made by casting electrically melted mineral materials such as quartz sand, for example, calcined clay, zirconium silicate, mixtures of mostly Al.sub.2 O.sub.3, ZrO.sub.2, and SiO.sub.2 (with traces of Na.sub.2 O and Fe). The temperature of the molten glass is between about 1300.degree. and 1600.degree. C., depending on the kind of glass. The soldier blocks, however, are subjected not only to considerable thermal stress but also to corrosion which is greatest in the region of the surface of the molten bath, the so-called level line. The corrosion also depends on the kind of glass in use.
In spite of a wall thickness of 250 to 350 mm, the life of such soldier blocks is between about 4 and 10 years, according to the kind of glass and the furnace throughput. In this period the material of the soldier blocks is worn away principally in the area of the level line, except for a small remnant of about 50 to 100 mm. The so-called "furnace campaign" is then ended if patching is not done. The molten glass must be let out and the soldier blocks, whose length may be between 800 and 2000 millimeters, depending on the furnace size, have to be replaced. The down time is a very considerable cost factor on account; of the considerable capital that is tied up and the high cost of repairs, but especially due to the loss of production, so that for a long time attempts have been made to prolong the "furnace campaign."
The material of the soldier blocks is a relatively poor heat conductor, which on the one hand reduces the loss of heat through the furnace wall, but on the other hand makes it difficult to cool the inside of the soldier blocks subject to the above-mentioned high temperatures. Usually the soldier blocks are flushed with cooling air in the area of their upper end. The cooling action, however, is poor because of the thickness or depth of the soldier blocks at this point, of about 250 to 350 mm, since a steep temperature gradient develops in the material on account of its poor heat conductivity. As a rule, therefore, the operators of such melting tanks abstain during the first one to two years from turning on the cooling air, and this, of course, accelerates the wear and corrosion. Not until a considerable part of the material of the soldier blocks has worn away is the cooling air started up, so that the retarding action against the corrosion does not start until a later period of time. The requirements for effective cooling on the one hand and sufficient thermal insulation on the other are to some extent diametrically opposite.
A patching method of the kind referred to above is disclosed in Trier's book, "Glas-schmelzofen Konstruktion und Betriebsverhalten," Springer-Verlag, 1984, pages 126 to 128, in which a fusion-cast repair block is placed on the outer side of the soldier blocks of undiminished cross section as soon as the wash-out in the area of the molten glass surface has advanced to such an extent that a temperature limit on the outer side of the soldier blocks is exceeded. This known measure, however, has no influence on the rate of erosion before the patching is done.
Patent DD-PS 240,538 discloses terminating a sandwich of an inner layer and an intermediate layer, both consisting of refractory material and together serving the function of soldier blocks, below the molten glass level and forming the tank chamber in the area of the molten glass level of superimposed bricks to form a so-called "edge layer." The bricks in question are C-shaped in cross section and carry inserts with cooling passages. No repair of the edge layer is provided for, and to prolong the duration of the furnace campaign it is proposed to construct the edge layer of a relatively thick, highly corrosion-resistant refractory material. After the edge layer has worn out it has to be replaced as a whole.
It is also known, through DE-OS 37 05 062 to place shaped bricks provided with recesses both on the inside and on the outside on top of the soldier blocks above the molten glass surface. The purpose of this measure, however, is to reduce the weight of the superimposed bricks while at the same time improving the thermal efficiency of the furnace. It is not possible to lengthen the useful life of the soldier blocks or the duration of the furnace campaign in this manner, since the shaped bricks are not in contact with the molten glass.